I. Field of the Invention
This invention relates to a method for manufacturing a heat-insulating member having a shell and a device therefor, more specifically to a method for manufacturing a heat-insulating member having a shell used for the housing or door of a refrigerator and other applications, including steps of injecting a foamable liquid composition into the shell of the heat-insulating member and foaming the composition in the shell, and a jig for holding the shell when the composition is foamed in the shell.
II. Description of the Prior Art
Presently, most of housing and doors of refrigerators, for example, are those that a foamed heat-insulating material, such as e.g. foamed polyurethane, is filled in a thin shell. Filled with the heat-insulating material, these refrigerator housing and doors are improved in heat insulating property, and can hence serve as heat-insulating members as well as their original functions.
Those heat-insulating members are conventionally manufactured by the following method. First, a hollow shell, which is not filled with any material yet, is placed in a lower jig made of metal, and is then pressed down by an upper jig also made of metal. These jigs are intended to hold the shell to prevent it from being deformed when the foamable liquid composition is later foamed in the shell. The shell is provided with an aperture through which the foamable liquid composition is to be injected into it afterward. Also, the upper jig is provided with an injection hole to open into the aperture of the shell, whereby the liquid composition will be injected.
Subsequently, the shell thus held in the jigs are heated in a furnace along with the jigs (preheating). Then, the shell, as well as the jigs, is removed from the furnace, and the foamable liquid composition is injected into the shell through the holes formed in the upper jig and the shell. Since the foamable liquid composition is prepared by mixing resin components with a foaming agent directly before the injection, the foaming of the resin components occurs substantially in the shell. The purpose of the aforesaid preheating is to accelerate the foaming reaction to assure the sufficient expansion of the heat-insulating material. If the preheating is eliminated, then the heat of the foaming material will be absorbed by the metal jigs and the shell, so that the material will solidify before it sufficiently expands. The preheating is necessary to avoid this.
Finally, to complete the foaming process, the heat-insulating member is heated again together with the jigs in the furnace (postheating), and then removed from the furnace, and the completed heat-insulating member is taken out of the jigs.
Including the steps of preheating and postheating, the prior art manufacturing process requires the furnace and fuel therefor. As a result, the price of the manufactured heat-insulating member will be increased. Made of metal, moreover, the jig is quite heavy (normally weighing about 300 kg) and hard to handle. Therefore, the material cost and manufacturing cost of the jig, as well as other associated expenses, will pile up to increase the price of product.